This defines the API for performing database actions. There are two levels
to this API: dealing with fields, and dealing with entities. In SQL, a field
corresponds to a column, and should be a single, non-composite value. An
entity corresponds to a SQL table. In other words: An entity is a
collection of fields.

Filters which are available for select, updateWhere and
deleteWhere. Each filter constructor specifies the field being
filtered on, the type of comparison applied (equals, not equals, etc)
and the argument for the comparison.